The present invention is directed to an assembly of collecting rods for use with a retracting head for the collection of pollen grains and fungal spores and is further directed to a method of making and coating such an assembly.
The Rotorod Sampler is a rotating-arm impactor that recovers airborne pollen grains, fungal spores and other particles by inertial sampling. It has been used extensively in the field of clinical allergy to perform pollen counts. The device has also found widespread application in the field of plant pathology for both basic science research and programs designed to mitigate crop loss.
The Rotorod Sampler is shown in FIG. 1 as 100. A small direct-current (DC) motor (not shown in FIG. 1) is equipped with an internal speed controller and is mounted in a protective housing 102 from which the motor""s shaft 106 emerges inferiorly.
A retracting head 108 is coupled to the shaft 106 with a specially machined aluminum shaft adapter (not shown). Spring-loaded pivot blocks 110, also machined from aluminum, hold two 1.52 mmxc3x9732 mm polystyrene collector rods 112, which are coated with an adhesive to retain impacted particles.
The springs 111 of the pivot blocks 110 maintain the collector rods 112 within the protected channel of the retracting head 108 when the sampler""s motor is idle. The collector rods 112 assume the position shown in FIG. 1 via centrifugal force when the motor spins.
Particle recovery on the collector rods 112 depends on two factors: particle impaction and particle retention. The former is governed by basic aerosol mechanics, the chief variables of which are (1) particle diameter, (2) particle density, (3) collector rod width and (4) collector rod speed. Additional considerations include the density and viscosity of the airstream carrying the particles.
Particle retention depends on (1) the kinetic energy of the particles striking the collector rods and (2) the properties of the adhesive coating on the collector rods. Silicone grease, which has been experimentally demonstrated to be superior to other compounds, is the adhesive of choice.
The collector rods 112 recover particles so efficiently that the adhesive gradually loses its ability with extended operation. One version of the Rotorod Sampler (the Model 40) therefore incorporates a duty timer (not shown) to facilitate intermittent sampling. For example, during the standard 10% duty cycle, the collector rods 112 spin for one minute and are then idle for nine minutes. That sequence repeats indefinitely until terminated by the user, usually after 24 hours.
The collector rods 112 are then removed from the sampler 100, stained with Calberla""s solution (which contains the red pigment basic fuchsin) and analyzed with a light microscope. Pollen grains and fungal spores are identified on the basis of their cellular morphology by trained technicians. The collector rods 112 are then discarded and not reused.
Users are currently required to apply silicone grease to the collector rods 112 by hand, by dipping a finger into the compound and then transferring the compound onto the collector rods 112. That process of greasing the rods causes four principal problems. First, it is time-consuming. Second, the results are inconsistent, both between technicians and for a single technician. Third, the optical properties during light microscopy are less than optimum. Pollen grains on areas with relatively thick grease are often not stained because they are inaccessible to stain. Fourth, microscopic analysis is more time-consuming. Frequent refocusing is required because the particles lie in multiple optical planes caused by inconsistent grease application on the collector rods.
Collector rods can be coated in a rapid, reproducible manner by dipping them into an emulsion of silicon grease and hexane (1:10 w/v). Hexane, which is highly volatile, rapidly evaporates, leaving a conformal coating of silicon grease on the collector rods. Such dipped collector rods have been demonstrated to be superior to hand-greased collector rods under experimental conditions. The principle advantages include (1) rapid preparation when dipped en masse, (2) less sample-to-sample variability in particle counts and (3) superior visual quality, thereby requiring less microscope time and reducing the number of unstained particles.
However, there is still room for improvement. In particular, there are still problems with packaging, shipment, and removal from the package by the user.
It will be readily apparent from the above that a need exists in the art to coat collector rods for the Rotorod Sampler or similar devices in a rapid, reproducible manner. It is therefore a primary object of the invention to provide a method to do so.
Further objects of the invention are to provide grease-coated collector rods that are conveniently packaged in a use-friendly manner, protected from the abuses of packaging, shipping and handling, and sequestered from dust and other airborne contaminants that might foul the rods before use.
To achieve the above and other objects, the present invention facilitates the preparation of a large number of collector rods at one time. Many (e.g., twenty) collector rods and a header to which they are attached are injection molded as a unit. In the preferred embodiment, several (e.g., ten) such units are snapped together via pins and sockets on the headers.
The resulting assemblage of collector rods can then be dipped en masse into a hexane-silicone emulsion. That process provides advantages in terms of significant time economies and in terms of uniform grease coating with little rod-to-rod variability within the assemblage.
Assemblages can be affixed with a solvent to the lid of a rugged, dust-proof storage container before dipping. Hinges on the lid facilitate access to the collector rods.
The header allows multiple collecting rods to be molded at one time. The groups can be assembled together by using the pins and sockets molded into the header. This molding process allows for equal distance surrounding the rods in all directions with the exception of the outside rods of the dipping group that do not have rods along the outer edge. The same is true for the rod surfaces on the outside edge marking the perimeter of the rods. This spacing allows for equal coating to occur. The header allows rods to be dipped, packaged, shipped and used without ever disturbing the collecting surface. The gate is designed to provide proper filling of rods in molding, firm attachment and easy breaking-off by the user.
A preferred embodiment of the present invention will be set forth in detail with reference to the drawings, in which:
FIG. 1 shows a conventional Rotorod Sampler with which the collector rods according to the preferred embodiment can be used;
FIGS. 2A-2C show three views of a group of collector rods according to the preferred embodiment;
FIG. 2D shows a detail of an insertion of one of the collector rods of FIGS. 2A-2C into the sampler of FIG. 1;
FIG. 3 shows a collector rod assembly including multiple groups such as the group of FIGS. 2A-2C; and
FIG. 4 shows a step in pre-greasing the collector rod array.